Nicola Edgington was ordered to be detained indefinitely after stabbing her mother nine times, but three years later she was released from a mental health unit to be cared for in the community.

After two years of being monitored by a psychiatrist, nurse and social worker, her life began to unravel. She sought help at a local hospital but after delays in admitting her, she walked out and attacked two women in the street.

Kerry Clark, 22, managed to fight her off and take a knife from her. But Edgington walked round a corner, took a knife from a butchers and almost decapitated Sally Hodkin, 58, in Bexleyheath, south-east London, in October 2011.

Edgington, 32, of Greenwich, south-east London, was found guilty at the Old Bailey of murder and attempted murder. She was remanded in custody to be sentenced at a later date to a life term when the judge will decide on the minimum term she will serve.

A statement from Mrs Hodkin's family said: "We cannot quite understand how or why Nicola Edgington was released back into society so soon after killing her own mother. Her release in 2009 didn't involve any independent psychiatrists or mental health tribunals; the Ministry of Justice simply followed recommendations from the Bracton Centre where she was being held.

"This cannot have been the right decision, otherwise we would not be here today. It is our opinion that this woman should never be released back into society. The public need to be protected from people like her."

But chief executive of Oxleas NHS Foundation Trust Stephen Firn said that a report into her treatment found that the decision to let her live in the community in 2009 was sound. Mr Firn said: "I am very sorry that this tragic incident happened and would like to express again my sincere condolences to the family of Mrs Hodkin.

"The trust inquiry report concluded that the decision to recommend to the Ministry of Justice that Nicola Edgington was discharged from the Bracton Centre in 2009 was sound and the care she received in the community following her discharge was of good quality."

A Ministry of Justice spokesman said: "The decision to discharge Nicola Edgington in 2009 was made by officials, without reference to ministers, under authority which is delegated as a matter of routine by the Secretary of State."